An Omni-Directional Treadmill (“ODT”) has proved its usefulness, especially when combined with a computer-generated, immersive graphics display. Such a combination permits a person to walk, run, or crawl on the treadmill while reacting to the visuals. Thus, the immersed person is able to navigate the virtual environment created by the computer in a way that is natural and easy to learn.
Previous ODT designs, disclosed by D. E. E. Carmein in U.S. Pat. Nos. 5,562,572 and 6,152,854 have shown the advantages of an ODT-based simulation system. Besides detailing various construction methods for these devices, these patents revealed novel and useful combinations of the ODT with various complementary components.
Earlier ODT designs had many parts, thus making manufacturing expensive and mechanical failure more likely. The more recent belt-based design has fewer parts and provides for a high velocity, highly dynamic device suitable for fast maneuvers and rapid speed. The penalty for a high-performance device is, again, high cost due to high forces. Need for higher-strength parts increases weight, which in turn increases the amount of power to effectively drive a system.
A typical configuration of the belt-based ODT design is disclosed in FIG. 19 of U.S. Pat. No. 6,152,854. The omni-directional treadmill is comprised of adjacent mini-treadmills or minisegments. Segments loop around the ends and meet at the bottom to form a complete circuit. The active surface is driven in the Y direction by one servomotor and in the X direction by another servomotor, and provides infinite omni-directional and bidirectional motion to a person navigating thereon.
A. Mitchell in U.S. Pat. No. 6,123,647 employs a side driver spline that engages teeth extending form each minisegment. This apparatus is expensive and difficult to execute because of the need for high tolerance and a synchromesh. The X drive actuation is challenging due to the nature of motion around the ends of the X circuit. A single attachment point drive for the minisegments causes the surfaces of the minisegments to instantaneously accelerate and decelerate as the minisegments enter and leaves the end return circuits.
Any ODT construction must actuate the Y belts in some manner. Any design that allows the Y belts to de-actuate and slow or stop must then drive them up to speed again as they re-engage the Y drive mechanism. This re-engagement causes both friction and noise, and under certain circumstances, it will compromise the desired surface velocity characteristics because the Y velocity will not achieve the desired speed.
ODT surface control schemes that employ position sensing to keep the user centered are inherently velocity limited because viable control schemes based on washout, or more simply, PID-type control, require space around the center for error to be generated. Once under speed, the user indicates additional velocity change by moving in the desired direction. A user already at the edge of the active surface may then be prevented from further movement towards the edge, and thus prevented from higher velocities. Highly dynamic movements may easily place the user next to an edge under these conditions. In general, the higher the desired speed, and the higher the accelerations, the larger the ODT surface must be. This is an inherent limitation of position-based control.
Existing ODT applications have done little to enrich the user's immersive physical environment. The invention proposes numerous devices and methods to enrich the user's physical experience.
Use of the ODT as a premium interface to immersive virtual worlds is uncharted territory. The current invention proposes several useful and interesting applications.